1. Field of the Invention
The present invention relates to a robot arm, and more particularly, to a brake device for stopping a motor of a robot arm from rotating as the robot arm is ceased.
2. Description of the Prior Art
A robot arm capable of taking a work piece and moving back and forth is usually applied to an automated factory for increasing a manufacturing efficiency. The robot arm needs not only a driving module for providing power, but also a reliable brake device to position the robot arm at a predetermined location precisely.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional driving module 10 of a robot arm in the prior art. The driving module 10 utilizes a motor 11 for driving a shaft 12 to rotate and a reducer 13 for reducing a rotary speed of the shaft 12 to output the power to move the robot arm. A brake device is disposed in the conventional driving module 10. A friction ring 14 is fixed on the shaft 12 and covered by a ratchet 15. The ratchet 15 is fixed on the shaft 12 by a friction force formed between the ratchet 15 and the friction ring 14. A solenoid valve 16 is further disposed for clutching the ratchet 15, so as to stop the ratchet 15 from rotating, such that the motor 11 is braked, which stops the robot arm from moving.
When it is desired to move the robot arm, the solenoid valve 16 is controlled to release the ratchet 15, such that the ratchet 15 rotates along with the shaft 12 driven by the motor 11. When it is desired to stop the robot arm, the conventional driving module 10 is braked, i.e., the solenoid valve 16 is controlled to clutch the ratchet 15 for stopping the ratchet 15 from rotating. Afterwards, the shaft 12 is stopped by a brake moment generated by the friction force formed between the ratchet 15 and the friction ring 14, which prevents the robot arm from moving. However, a rotating torque of the shaft 12 will overcome a maximum static friction force formed between the ratchet 15 and the friction ring 14 due to excessive inertia of the moving robot arm, such that the friction ring 14 still slides relative to the ratchet 15 and rotates along with the shaft 12. Since the shaft 12 is not stopped from rotating forcedly, the robot arm is prevented from being damaged.
However, the ratchet 15 and the friction ring 14 of the conventional driving module 10 are fixed on the shaft 12 directly, such that the brake moment generated by the ratchet 15 and the friction ring 14 is quite small because the ratchet 15 and the friction ring 14 are too close to the shaft 12. When it is required to increase the brake moment for stop a larger or faster robot arm, it is usually to increase the friction force formed between the ratchet 15 and the friction ring 14 due to a constant distance between the solenoid valve 16 and the ratchet 15, and limited mechanical space. In other words, a prepressing force of the ratchet 15 acted on the friction ring 14 is increased for increasing the friction force and the brake moment. Therefore, it is required to replace materials and parts to endure higher stresses, which raises manufacturing cost and difficulty of assembly.
Therefore, there is a need to design a brake device of a robot arm for solving the above-mentioned problems.